The present invention relates to a rocker arm and a manufacturing method thereof.
In general, the rocker arm includes a body and a roller pivotally attached to the body through a support shaft. The body includes a pair of side walls opposed to each other in the axial direction and a pair of connecting walls for connecting the side walls with each other at both end portions of the side walls in the longitudinal direction.
The valve engaging portion is constituted by valve guide walls, which are arranged at one end side of the side walls in the longitudinal direction, and a connecting wall arranged on one end side for connecting both the valve guide walls. The pivot receiving portion for receiving an upper end portion of the lash adjuster is formed on the connecting wall on the other end side of the side walls in the longitudinal direction.
The body of the above rocker arm is manufactured by means of press forming in some cases. Concerning the procedure of manufacturing the body, one metallic sheet is punched by means of press forming so as to form it into a metallic sheet member having a predetermined shape. Then, this metallic sheet member is folded and formed into a substantial U-shape as shown in FIG. 11. After that, in this U-shaped metallic sheet member, a valve engaging portion is formed by using the die 50 having a predetermined shape. This die 50 is integrally formed to have a recess portion 53 into which a pair of side walls 51, which are opposed to each other, and the connecting walls 52 are inserted.
In the case of forming the valve engaging portion by using the integral die 50 described above, there is a possibility that stress concentration is caused in the corner angle portion 53a of the recess portion 53 when the die 50 is given a force. Therefore, cracks tend to occur in the die 50 originating at the corner angle portion 53a of the recess portion 53.
Therefore, it can be considered that the die 50 is divided as shown in FIG. 12. This die 50 includes: a pair of outer dies 55 to push the side walls 51 laterally; and an inner die 56, separated from these outer dies 55, to form the connecting wall 52 between the outer dies 55 and the inner die 56. These outer dies 55 and the inner die 56 are divided on the dividing lines 57 that is formed at a portion corresponding to the corner angle portion of the side wall 51. According to the above constitution, it is possible to prevent the occurrence of cracks in the die 50.
However, in the case where the die 50 is divided into the outer dies 55 and inner die 56 as described above, when a force is given to the outer dies 55 and inner die 56, there is a tendency that both the dies 55, 56 slip relative to each other and a gap is formed between the dies 55, 56.
Therefore, when the valve guide walls 51 and the connecting wall 52 are formed, metallic material may plastically flow and get into the gap formed between both the dies 55, 56, and the metallic material, which has plastically flowed in this way, may remain as molding flash in the portion corresponding to the corner angle portion of the side wall 51. The thus formed molding flash can not be removed in the finishing work conducted in the later process in some cases. Therefore, the thus formed molding flash is separated from the body during the use of the rocker arm and attached to parts arranged in the periphery.